Electron discharge tube



March 12, 1940. V R, HELBY 2,193,539

ELECTRON DISCHARGE TUBE Original Filed April 6, 1936 3 Sheets-Sheet 1 ELECTRONIC STREAM Za T 5 A/VODE I0 I ELECTROSTATIC L DEFLEUII&, INPUT/v0.1 g PLATES 8 ;QL INPUT N0.2 I g L \F/RSTANODE l T"\\CONTROL GRID \CATHODE 20 -l'|'|'l T;

ro HEATER SUPPLY I 1 1 2 INVENTOR ROBERT E. SgL-MW March 12, 1940.

R. E. SHELBY ELECTRON DI S CHARGE TUBE Original Filed April 6. 1936 e/AND 92 90 TOINPUT A/OJ e! g 5 Sheets-Sheet 2 PHASE our 0F PHASE pf WA ourPur AMPL/TUDE 1kg, 3a, 20 INVERSL Y PROPORTIONAL r0 FREQUENCY FOR. AMPL/ T U05 FREQUENCYMflDULAT/M/ MODULATOR CARR/ER WAVE 30 g, AMPLIFIER AMPLIFIER 411/0 32 A COEEECT/OA/ 2 c/ecu/r 042121512 FROM MODULA r/0/v gg fg gia fl TED FREQUENCY STABILIZED SIGNAL sowzce INVENTOR ROBERT E. SHELBY ATTORNEY March 12, 1940. R. E. SHELBY ELECTRON DISCHARGE TUBE Original Filed April 6. 1936 3 Sheets-Sheet 3 QMERUWQ a mu Mu mm INVENTOR ROBERT E. SHELBY kmkmu ATTORNEY Patented Mar. 12, 1940 J UNITED STATES PATENT OFFICE ELECTRON DISCHARGETUBE I g I Robert Evart Shelby, Teaneck, N. J; assignor to Radio Corporation of America, a corporation of Delaware Original application April 6, 1936, 'seriaiNo;

72,916. Divided and this application June 30, 1939,Serial No. 282,183

1- 1 Claims. (01. 250-151) The method and means of the present inven-, tion is proposed mainly as a method and means for frequency or phase modulating a'cai'rier' sigin which the form of the modulated current wave may be represented by the equation? shifting network used in the circuit of Figure 3;

nal obtained from an oscillator of cohstantfref f Sin(wi+HSiI1 H (2) quency and phase. The oscillations may be obtained froma crystal 'controlled'oscillator. How-i 1f the odulated carr er wave has the form ever, various embodiments of the underlying prin P wot and the modulatlon 'Slgnal has m Ciple a be used for-other purposes such as Sm l I amplitude modulation, current limiting, frequency The cymbols of Equatlons (1) (2)1193"? conversion, rectification, etc. This application isthe following means: a

a division Of y United States pplication zp=instantaneous value of phase modulated cur- #72,9 16, filed April 6, 1936, both having features" rent. common with my United States application if=instantaneous value of frequency modulated #100,627, filed September 14, 1936, nowPatent nt $2,171,150, issued August 29, 1939. I zoo-21itimes carrier wave frfequency-in cycles In one system of frequency modulatlon known per second. u i in'the art, modulation is achieved by adding two :2 tim s modul tion signal freq ency in, voltages of the same frequency which have 'a cycles per second. i v 2o Dhase difierence of 90, one voltage having cont: ti in seconds, 1

stant aznlplillide and the other varying in ampli- Ap, Aj, kp, Icj and 950 are arbitrary constants.

ude Wi e modulation signal. This method i i n has: thedi'sadvantage of series distortion unless g; figg z iiiggfi gg g fg i f fi gggg the maximum phase shift is limited to small-an- Theory of Electron by I. G Maloff g t f the order T reaspn that D. W. Epstein, Proceedings Institute of Radio l dlstortlon is produced is that the amplitude of I i ngineers, December, 1934, page 1386. 1 the modulatlon Signal (or any glven frequency) In describing my invention reference will be is proportionalto the tangent of-the angle "of i made tothe attached drawings whreim phase shift and not '9P the g Figures 1 and 2 show an electron device, or -sitar:restaurateursraisins;. or a with the present invention and having a novel piimates the angle closely enough to prevent anode or target or plate The discharge device serious distortion but above about 30 the distor- Shown connected in novel modulation tion increases rapidly. In order to obtain a p worthwhile shift at the finalzcarrier frequency 1 i e the shift in. the modulated stagenis 300 "o 113 3132 123233;; iz ii gh o s fijt less it is necessary tomodulat e a relatively low I the points on the useful Surface are equi distanit frequency carrier and employ frequency multifrom the electron stream ori 1 v p-lvmatlpn of f f rang v t i Figure lb illustrates a modified electron tube 40. f d p1 opqsed i g e l' ave or gunwherein the surface of thetube envelope mmtation. Theoretically it will give distortionvisicoated with a conducting material collect less" phas.e Shlfl? of F t times 360 though electrons which pass the targetanode or are of" tually this may be limlted by structural difiiculasecondary nature; l

hes to w .comPlete m v 1 1 Figure 2a is an additional modification of the '46 In F1118 speclfic-atwn h term Phase f? target. The target of 2a includes pairs ,of ele- 4 tion unless otherwise specifically stated, refersments similar y pairs f elements? Figure I to modulation of the kindin which the form of A target as shown i Figure 2a may be used the modulated Current Wave m be represented when multiplication of frequency, or' the same byeth e equ onr a a p with modulation, is desired; 7 I D 7 1 Figure 3illustrates by line diagram my novel V TA n(w p 1 0 8111 M circuit for producing and applying-deflectingpoif the unmodulated carrier wave has the form "tentials to the electrodes of the novel electron sinwot and the modulation signal has the form dischargedevice of Figures 1 and 2 p sin pt; and the term frequency modulation Figure 3a shows in detail, one form of phase 68 employed herein, refers to modulation of the kind I said tube.

ments of a complete modulation system arranged in accordance with my novel concept.

structurally the device consists, as will be seen by reference to Figures 1 and 2, essentially of an electron gun 4, two sets of electrostatic deflecting plates 6 and 8 and a target anode 10 of special design, enclosed in an evacuated container of suitable size and shape. One typical arrangement has been shown schematically in Figure l for purposes of illustration. It will be seen at once that the device illustrated is similar in some respects to. a conventional cathode ray oscillograph tube. One of the fundamental differences between the present device and known devices, is the novel design of the target anode it]. Figure 2 illustrates one form which the target anode may take. It consists of two (or more) metallic elec-.

trodes M and is with curved boundaries, upon which electrodes the electrons from the electron gun impinge. The electrodes it and I6 may consist of metallic plates or meshes or metallic deposits on the tube envelope or on a support in Where the elements i i and it are of mesh, a collecting electrode may be located back of these targets and properly charged relative to the other electrodes as shown in Figure 1b. In order to obtain frequency or phase modulation of a carrier Wave in which the angular phase shift of the wave is a linear function of the amplitude of the modulation potentials the inner edges of the plates i and 56 have a curvature defined by the polar. equation which defines an Archimedian spiral. In this equation 7" is the radial distance from the original 0 which is the focal point of the curve r=a0, to any point on the curved edge of the plates, 0 is the angular displacement measured in radians of the same point from a selected datum line which is in the plane of the target anode ill and passes through'the origin 0, and a is a design constant related to the number of turns of the plates l4 and i8. In other words, r and 9 are the usual parameters used in polar coordinates. In the preferred form, the periphery of any plate adjacent the edge of the adjacent plate defined by r=a0 may be defined by the same equation with reference to other properly selected datum lines.

In operation the electron stream is deflected by plates 6 and 8 in such a way that it traces out a circle on the target, or anode plates l4 and it,

the diameter of the circle being a variable which is directly proportional to the instantaneous value of the modulating signal potentials. When controlled in this way the electron stream may" described, provided the deflecting plates 6 and 8 are properly energized. Operation of the system will now be'described more fully.

The electron gun iscontrolled and focused by adjusting the direct current potentials applied from any suitable source or sources to the oathode, control grid, screen grid and first anode,

just as inthe case of oscillograph tubes and kinescopes. Sources 29 and 22 have been shown for purposes of illustration. The electron stream is focused on the target anode comprising sections Hi and I5, and when there is no deflecting'voltage applied to the electrostatic deflecting plates 6 and 8 it strikes the exact geometrical center of the target anode that is at origin 0. In a preferred form the deflecting plates 6 and 8 are substantially displaced by 90. In this case the carrier wavesapplied tothe sets of 'plates should be displacedby 90. Of course, other angular relations between the sets of deflecting plates 6 and 8 may be used, in which case the phase relation between the applied waves may be changed. The essential requirement is that the electron stream be caused to describe a circle on the target anode; with the plates shown, if linear modulation is desired. The inputs, which consist of two carrier waves of equal frequency and almost equal amplitude but differing in phase and having the same percentage amplitude modulation, are appliedto the two sets of electrostatic deflecting plates.

Figure 3 illustrates by line diagram one means of supplying the inputs to the deflecting plates 6 and 8. In Figure 3 carrier wave oscillations from any source are supplied to the input of an amplitude modulator 2B which is also connected to any source of modulating potentials. The output of the modulator is connected to an amplitude regulating potentiometer P! which is connected-to a phaseshifting system or network 22 This network may take any form, the essential feature being thatthe output thereof supplies two portions of the amplitude modulated wave in phase displaced relation. The phase displacement is 90 when the deflecting plates 6 and 8 are at right angles and linear modulation is desired. One output goes directly to one set of deflecting plates. The other output is fed to an additional potentiometer P2 which is connected to the other set of deflecting plates. A preferred form of phase shifter has been shown in Figure 3a. In this phase shifting circuit the amplitude modulated radio frequency or carrier frequency waves are applied to input terminals and from said terminals to a resistanceipil in series witha condenser .32. By adjusting the condenser 32 and selecting the value of 30 the desired phase relation between 8! and 62 can be produced. The oscillations may be modulated by keying, by voice frequencies, by television or facsimile signals or ulating potentials are applied in theircharacteristic form to the stage 2%! where amplitude modulation takes place. If frequency modulated output is desired the modulating potentials are distorted or corrected in such'a. manner thatthe' potentials applied to the stage 20 are attenuated in proportion to their frequency.

The produced phase 'or frequency modulated output appears in the circuit including one or both of the target electrodes i l and 16, across the impedance Za or any portion of Za. If 'Za is a pure resistance the output voltage appearing across it will be a flattopped wave of constant amplitude having frequency or phase modulation proportional to the amplitude modulation of the input, and a fundamental frequency equal to thatof the'input'carrier. By use of suitable reactance elements instead of a resistance 'Za may,

be tuned to the fundamental or any one of its harmonics. By using .a target anode composed of a larger number of curved sections the fundamental frequency of the fiat-topped output wave may be made any desired multiple of the input frequency. Thus, it is seen that, if desired, frequency multiplication may be obtained during tiometer P2 of Figure 3 are adjusted so that the electron beam from the cathode of 4 describes a1 circle on the final anode target and in particular, on plates i4 and IS, the center of said circle coin ciding with the point 0. If the potentiometer Pl is adjusted so that this circle is of the size desig-. nated by Cl in Figure 2 then the voltage appearing across Za will be as shown in curve a of Figure 4. Note that the electron stream passes from I one segment of the target anode to the other segment at points pi and plfl. If now, the two deflecting voltages are decreased say, for example, roughly percent vby changing potentiometer Pl, all other controls being left the same, the locus or path of the electron stream on the target anode will be C2 of Figure 2, and the voltage across Za will be as shown by curve bin Figure 4. The electron stream now passes from one segment of the target anode to the other at points 702 and p2. Likewise, if the potentiometer PI is adjusted to give higher voltages, say, for example, voltages 50 percent greater thanthose which gave the locus Cl, then C3 will be the new path or locus of the electron stream on the target, and the electron stream will pass from one target anode segment to the other at points 103 and p3 and the voltage appearing across Za will be as shown by curve c in Figure 4. Now if?! is reset so that the electron stream path'falls on Cl and, for example, a fifty percent amplitude modulation is then applied to the carrier in the manner indicated by Figure 3 the locus or path of the endpoint of the electron stream will vary between the limits C2- and C3 and the outputwav will shift in phase between the limits in dicated by curves b and c of Figure 4. In thissystem adjustment of circuit constants and monitoring of the system is facilitated by coating the' target anodes or plates with willemite or other sub stance which fiuoresces under the bombardment of the electron stream. Although as pointed out above, frequency or phase modulation accompanied by frequency multiplication may be accomplished when the target is as shown in Figure 2 of Zn is reactive I provide other means for accomplishing these results. By providing a target as illustrated in Figure 2a having a plurality of pairs of ele-' ments l4, l4 and l5, l6 with boundaries similar to the boundaries of the corresponding'plates of Figure 2, the phase or frequency modulation and frequency multiplication is accomplished simultaneously in the tube. The number of elements may be increased indefinitely within practical limits. When two pairs of elements are used as shown in Figure 2a, alternate onesarejoined as shown at H0 and H2. For simplicity the circles Cl, C2 and G3, etc., have been omitted in Fig ure 2a.

Although my invention will be clear to those that the circuit diagrams do not become too in-- particular to Figure 5, 4(lv desiredfrequency of constant frequency. Al-

, though I have shown the oscillator as being of,

p the crystal control type it will be clearly under stood that any means, such asa long line control frequency oscillator or an electron coupled oscillator may be utilized in place of the crystal oscillator shown The output electrodes of, the crystal oscillator are connected with aYbuffer amplifier stage comprising an electron discharge device 42 and are supplied byway of a blocking condenser 4i and transformer from the output electrodes of said buffer amplifier stage to the control grid electrode of a furtheramplifier 44. Electron dis", charge device 42 may beof the screen grid type as shown, wherein the screen grid serves toshield the outputelectrodes and circuit from the input electrodes and driving stage or this tube may be of the three electrode type and may be connected in a neutralized circuit. The amplifier 44 may also multiplyv the frequency of the impressed oscillations while amplifyingv the same. In this,

case the input circuit 45 of=-4.4 istuned to the frequency at which 42 operateswhile the output circuit 46 is tuned to a harmonic of said frequency. This tube 44, has been shownas being of thevpentode type although it will be realized that any other appropriate tube may be used in place of the one shown. The anodeelectrode of thetube 44 is coupled to a tuned circuit 46 the winding of which forms the primary winding of atransformer 56. The secondary winding of plate of one of the sets of deflecting plates 6 and 8, sayof plates 6. tuned circuit is'connected witha phase shift- The other terminal of the ing circuit 58 comprising an inductance 51 shunted by a: variable condenser 59 and a variable resistance 80. One end of-this phaseshifting circuit 58 is connected as shown to ground by way of a resistance 5! anddirectly to one of the plates of theother set of deflecting plates, say

. plates 8. The other terminal of the phase shift ing circuit 58 is connected to one of the remain ing deflecting plates of the pairs of plates '5 and 8. These remaining deflecting plates are also connected to ground by way of resistances 6i and 62. Thus, we have a series circuit including the capacity between the plates 6, indicated by the to resonance at the frequency of the oscillations applied to 55 and thereby made to represent" a pure resistance at this frequency. The variable resistance is used to control the amplitudeof the potentials applied to the deflecting plates .8.

When adjusted in such a manner this phase shifting circuit is the equivalent of that shown in Figure 3a. Any other appropriate phase shifting meansmaybe used.

Operating potentials for the tubes 40, 42,44

and 12 may be supplied from any suitable source.

Likewise, operating potentials for the cathode raytube [may be supplied from any source. I prefer, however, to use a rectifier'such as illustrated at R with its positive side grounded and its output connected to the electrodes of 4 as shown. This circuit, it is believed, needs no explanation.

Up to this point, I have described means for applying high frequency or carrier frequency oscillations in phase displaced relation between the plates 8 and 6 of the electron discharge device of the present invention. I will now describe the means for amplitude modulating the oscillationsbefore they are phase displaced and applied to said deflecting plates.

Modulating potential may be applied from any source to the primary winding of an audio frequency trans-former AFT, the secondary winding ofwhich is coupled as shown to a potentiometer resistance PR. A point on the potentiometer resistance PR is connected as shown by way of the resistance 63 and condenser 65 to the control grid of a modulation frequency amplifier 68. The resistance 63 and a portion of the potentiometer resistance PR is shunted by a condenser 64; The output of the modulation potential amz-plifier 68 is connected as shown to a direct current plate circuit comprising resistance 6'! and to an audio frequency circuit comprising a coupling condenser 69 connected to a radio frequency choke RFC which is in turn connected to the anode of the amplifier or multiplier 44 to accomplish in said tube anode modulation of the amplitude of the carrier wave being applied to the phase shifting circuit.

The phase modulated or frequency modulated oscillations produced on the target anode l appear in the circuit it and are impressed from the circuit Ill on to an additional amplifier '12.. The circuit IQ may be tuned to the fundamental frequency, that is, the frequency applied to the defiecting electrodes of the tube 4 or to a harmonic thereof. The circuit T0 is coupled to the input electrodes of amplifier 12, the output electrodes of which may be connected to a utilization circuit 8! directly or by way of a frequency multiplier 14' and a further amplifier shown dia- If desired, the

grammatically in a rectangle Iii. circuit H1 and its coupling to the tube l2 may be replaced by a resistance as in Figure 1 in which case the frequency or phasemodulated wave en ergy from the target anode ill will be impressed on tube 12 with no appreciable filtering. This energy then may be frequency multiplied and amplified for use by any one of several means well known to the art. The output or utilization circuit B0 may comprise radiating means or lines over which the phase or frequency modulated waves may be transmitted.

When the waves are to be frequency modulated the resistance 63 connected in the input circuit ,of amplifier 68 may be of high impedance to the modulating frequencies and in particular to the higher modulating frequencies, while the condenser Ei i may be of low impedance to the modulating frequencies and in particular, of low ime pedance to the higher modulating frequency poportions-of the circuit between said points.

In the electron tube 4 of Figure 5 I increase the power output of the electron tube by pro-.

viding a second anode 98 located adjacent the two target anodes. In practice, 90 may be a conducting element located in the tube or may consist of a-deposit or coating on the tube envelope as shown at C in Figure lb. The electrode 96 is maintained at a potential more .positive than that applied 'to electrodes II]. This anode or coating. or collecting, or return electrode 9D collects the electrons emitted from the target anode ill by the phenomenon of secondary emission occurring when the primary electrons of the beam strike the target. The electrode 90 also collects any electrons free in the tube and there may be considerable in the case electrodes 30 are grids or meshes. The electrode 90 is in this particular embodiment in the current path of both electrodes It and the circuit Ill and since the secondary emission may be made greater than the primary emission, the current output may obviously be increased. When this is accomplished to the desired extent the number of stages between the'output circuit 10 and the utilization circuit may be materially reduced. The stages remaining may operate to multiply the frequency of the phase or frequency modulated oscillations produced to, a greater extent when a'highfrequency output is desired. The manner in which this phenomenon is used to enhance the power output has been disclosed more in detail in Headrick, United States application #673,570 filed May 30, 1933.

It will be understood that many variations of the above described apparatus are possible. The fundamental principle involves the use of an electron gun, or other source of electrons, and an anode of such configuration that the voltage fluctuations applied to one or more elements of the tube are translated into phase, frequency or amplitude modulation in the anode circuit, the type of translation being dependent upon the configuration of the anode as well as upon the nature of the input voltages and the method of applying them.

The amount of maximum phase shift in the device described above will be determined by the curvature of the anode platesthat is, it will depend upon the'value of a in Equation 3. For the anode illustrated in Figure 2 the phase shift is plus and minus approximately 90 when the input is amplitude modulated 50 percent. Uh der the same conditions, amplitude modulationof '75 percent on the input will give phase shift of approximately plus and minus 135, etc.

Electromagnetic deflection of the electron stream may be utilized instead of electrostatic deflection" as described above.

Instead of amplitude modulating the voltages used to deflect the electron stream, these voltages may have constant amplitude and the modulation. voltage may be introduced (in proper ratio) into the accelerating electrode circuits of the electron gun. Variation of the accelerating electrode voltageswill cause the sensitivity or Variationsof voltages on two or more of the electrodes of the electron gun in proper .ratio) is necessary to preserve sharp focus of the ielec-- tron stream throughout the modulation cycle.

vIn Figure 1, the target anode is-indicated as havingf'a planesu'rface. In one type of 'this modulator tubekthe target anode Hlhas been constructed "with a curved surface" (saucershaped) as shown in Figure la, so thatthe' electrons from the electrongun always travel 'very nearly the same distance before striking the target, regardless of the amount of deflection of the electron stream from its undeflected path. In this case the curvature of the boundaries of the target electrodes is not completely represented by the simple Equation 3. In this par ticular tube the curvature of the boundaries was made such that the phase shift in theoutput' wave is directly proportional to the change'in deflecting potentials causing the phase shift.

Auxiliary electrodes may be added to the de vice described for control or monitoring purposes.

For example, a willemite screen such as that used in cathode ray oscillograph tubes might, be provided beyond the target anode, so that the electron stream would produce a pattern upon it when it passed between segments of the target or beyond the outer edges of the target plates.

Additional electrodes, located in the same plane as the target anode, but electrically separate from it, might be usedfor adjusting the modulator and also for indicating over-modulation. Such an electrode, of small area, located at the geometrical center of the anode (where the anode plates are cut away)) would be .useful in centering theelectron stream. A narrow annular ring around theoutside of the main anode could be used in connection with adjustment of the phase shifting network to obtain circular deflection of the electron stream. Other auxiliaries will undoubtedly suggest themselves.

The description so far has related to the production of modulation in which the phase shift is proportional to the-modulating voltage, but the i principle is quite flexible in this respect. By use of a properly shaped target, the phase shift may be made almost any function of the modulating voltage, this being determined by the curvature of the boundaries of the targetxplates and/or the nature of the curve described on the anode by the electron stream.

The amplitude of the output voltage wave may be varied independently of the frequency (or phase) modulation by varying the direct current potential applied to the control grid of the electron gun. If it is desired to amplitude modulate the output wave in addition to or instead of frequency (or phase) modulating it in the manner described this maybe done readily by applying the amplitude modulation signal to the control grid, provided the electron gun is so constructed, adjusted and operated that the rate of electron emission from the gun is a'linear function of control grid ,voltage over the operating range. One manner in which the output Wave may be modulated in amplitude has been illustrated in Figure 5. Other means will be obvious to those skilled in the art who have read this specification. In Figure 5 a second source of modulating potentials modulated :by'av'second signal from'lllll.

platesspiralling outwardly fromsaid focal point.

. target electrode in the path of said emission from ber I grid of thefgunt. The wave 'maynowbee .amplitudemodulated-only by'potentials from I or. may be phasezgor frequency. modulated only by-potentials fromcAFIlbr a phase modulated :Wavecarryingsignals from AFT may be amplimaybe connectedawit-h the primary winding of a transformer :Jfillandt thefsecondary winding of this transformer may be switched into the direct current. circuitgbetweenthe cathode and numj 5 tude modulated byiother signals from liiil so thatr 10 multiplexing; of signals on single carrier "is lated-:jby one 'signalfrom AFT and amplitud Of course,- I contemplate amplitude modulating;

-- by additional. signals the frequency. multiplied phase or frequency multiplied wave in i2, or 14,

or 16, or at the output of it, when multiplexing ofsignals is desired.

What is claimed is: i 1. An electron discharge device having, a tarabout a focal point, a portion of the boundaries of said surface being defined by r=a0; where r=radial distance from said focal point, a is a constant and 0 is angular deviation from a straight datum line through said focal point along which r=zero.

2. An electron discharge device having a cath- 'get comprising at least one surface arranged ode ray producing element and a target comprisabout the focal point of said ray, each of said 4. An electron discharge device having a targetcomprising a plurality of elements arranged in a substantially saucer-shaped surface about a flat target electrodes spiralling outwardly subv1 stantially at right angles to the normal path of emission from said emission element as a focal point, a pair of similar deflecting electrodes adjacent the path of said emission and a collecting anode adjacent said target electrodes.

6. In an electron discharge device, an electron emission element, pairs of deflecting plates, a

said element said target electrode comprising similar conductive plates of considerable surface 'area having inner and outer curved peripheries points along which peripheries are at different distances from the normal path of said emission and an anode located adjacent to said target electrode. I p

7. In a discharge device, an electron emitting electrode, a target electrode comprising a plate, a portion of the edges of which is defined by T=.a0 (Where r=radius from the electron stream focal point, a is a constant, and 0 is angular deviation from a..straight.,,line through said focal point where r='0), and a pair of deflecting electrodes trode and said target electrode.

8. An electron discharge device having an electrode element of curved contour such that, points of intersection of an edge of sail; element with adjacent the path between said emitting elecr trary direction from the center of the circles increases linearlyasthe radius of the circles-increases.

9. An electron discharge device having an'elec- 'trod'e in the form of a conducting element lying substantially in a plane normal to the 'path of discharge of saiddevice, said element having a contour such that points of intersection of an "edge'of said element with concentric circles of concentric circles of increasing radius are points Whose position angles with reference to an arbitron emission element adapted, when energized,

to produce an electron'stream or'a"ray, and a target electrode located normal to the path of said ray,-said target electrode comprising'a plurality of'conducting surfaces the peripheries of which spiral outwardly from the'normal point of intersection of said ray and said surface.

11. An electron'discharge device having an electrode element of curved contour such'that points of intersection of an edge of said element 'l with concentric circles of different radii are points whose position angle changes linearly with reference to anarbitrarydirection from the center ofthe concentric circles a's'the'radii of 'the circles change.

' ROBERT EVART SHELBY. 

